A comparative study on involvement of tPA activity in ovulation induced by hCG and GnRH agonist in hypophysectomized...

A GnRH agonist (5-50 micrograms) is capable of inducing ovulation in PMSG-primed hypophysectomized immature rats, as is the case in hCG-induced ovulation, but 2-4 h earlier than hCG. GnRH-induced ovulation is effectively blocked by the concomitant administration of the GnRH-antagonist which failed to interfere with hCG-induced ovulation, indicating that GnRH and its agonists do not share a receptor with LH/hCG. Like hCG, GnRH is also capable of inducing tissue type (tPA), but not urokinase type (uPA) PA. The plasminogen activator activity in ovarian homogenates and the granulosa and theca-interstitial cells increase in a time-dependent manner, reaching maximum levels just prior to ovulation. Similar to hCG, GnRH also increases tPA activity in cumulus-oocyte complexes in a time-dependent fashion.